Conventionally, this kind of data transmitting apparatus and data transmitting method are described in, for example, Japanese Patent No. 1647396. FIG. 1 is a block diagram illustrating the configuration of each of a base station apparatus and a mobile station apparatus, which are used as conventional data transmitting apparatuses.
The base station apparatus 1 illustrated in FIG. 1 includes a buffer 10, a format converter 11, a spreader 12, a modulator 13, a variable gain amplifier 14, a demodulator 15, a despreader 16, an error detector 17, and an SIR detector 18.
An output signal of the variable gain amplifier 14 is transmitted from an antenna via a circulator 19. Moreover, the signal received by the antenna is outputted to the demodulator 15 via the circulator 19.
Moreover, the mobile station apparatus 2 illustrated in FIG. 1 includes a buffer 30, a format converter 31, a spreader 32, a modulator 33, a variable gain amplifier 34, a demodulator 35, a despreader 36, an error detector 37, and an SIR detector 38.
An output signal of the variable gain amplifier 34 is transmitted from an antenna via a circulator 39. Moreover, the signal received by the antenna is outputted to the demodulator 35 via the circulator 39.
According to the above configuration, when data is transmitted from the base station apparatus 1 to the transmitting station apparatus 2, data is subjected to buffering by the buffer 10 and the resultant data is formatted to a given format by the format converter 11 and the resultant data is spread by the spreader 12. A spreading factor used at the spreader 12 is determined when a channel is assigned, and the determined spreading factor is fixed afterward.
Spread data is modulated by the modulator 13, and modulated data is further amplified by the variable gain amplifier 14 and is transmitted from the antenna via the circulator 19.
This transmission signal is received by the antenna of mobile station apparatus 2 and is inputted to the modulator 35 via the circulator 39. Then, after the inputted signal is demodulated by the modulator 35, the modulated signal is despread by the despreader 36. This obtains received data.
At the time of this reception, the SIR detector 38 outputs a TPC command (Transmission Power Control signal) that makes a request of the transmitting side to increase/decrease a level in accordance with the received level.
Moreover, when detecting an error from an error detection bit of received data, the error detector 37 outputs a retransmission request signal.
The TPC command and retransmission request signal are transmitted to the base station apparatus 1 via the format converter 31.
When a request for an increase/decrease in a level with the TPC is made, the despreader 16 of the base station apparatus 1 varies the gain of variable gain amplifier 14 as required in accordance with the request.
Moreover, when retransmission is performed, the base station apparatus 1, which has received the retransmission request signal, retransmits transmission data.
Such control is provided to the base station apparatus 1 from the mobile station apparatus 2 in the similar way.
Thus, according to the conventional data transmission method, the spreading factor is fixed to perform data transmission. Namely, though the retransmission request is made, the conventional data transmission method uses such a spreading factor that is held constant to obtain reception performance at one time. For this reason, high-speed transmission power control is performed to maintain the quality.
However, in the conventional apparatus, its performance is largely influenced by the accuracy of transmission power control because CDMA system is used. Particularly, delay in control at a high-speed fading time causes a crucial problem. Namely, unless transmission power control is executed with high accuracy according to the TPC command, a desired quality cannot be maintained. Moreover, the apparatus does not keep up with high-speed fading in some cases. This causes a problem in which transmission efficiency decreases.
Since the fading variation speed becomes fast as the use frequency band increases in the mobile communication system, quality deterioration will increase extra in the future relative to the current state. Also, since TPC command must be frequently transmitted, its processing time increases and transmission efficiency is expected to further deteriorate.
Regarding the fixed spreading factor, on the assumption of the line whose condition is poor to some extent, the spreading factor must be fixed to be high to some extent. This causes a problem in which a symbol rate cannot be increased so that high-speed transmission cannot be performed, resulting in deterioration of transmission efficiency.
Moreover, if transmission power control is performed to maintain the average quality, the user having a poor line quality needs a large amount of transmission power and the transmission amplifier must deal with a large dynamic range. Furthermore, in the case of a good line condition, though transmission power can be dropped, average transmission power is lost. For example, in the case where the possibility that data transmission will be performed with the half power of standard power is equal to the possibility that data transmission will be performed with the double power of standard power, there is a problem in which large average transmission power is always needed as compared with transmission with standard transmission power. Furthermore, there is another problem in which the dynamic range of an interference signal is increased by transmission power control so that the large dynamic range of the demodulation system is required.
Moreover, the spreading factor can be adaptively changed, but the spreading factor must be transmitted to the communication counterpart for this purpose. It is difficult to estimate an optimal spreading factor to perform this transmission. Even if such estimation can be carried out, this prevents high-speed communication when delay time for estimation increases. Furthermore, in the case where information for estimation is transmitted, the entire amount of signals increases. This causes a problem in which transmission efficiency deteriorates.
Moreover, at the present time, transmission from a plurality of antennas is also carried out in W-CDMA. However, even if transmission from a plurality of antennas is thus carried out, there is a problem in which performance as transmission diversity is not so largely improved.